Negative contrast agents for magnetic resonance imaging comprising barium sulfate and a clay

Abstract

A negative contrast agent for MRI is an aqueous suspension having a quantity of barium sulfate between 25 and 30 percent by weight and a quantity of bentonite between 2.5 and 3.5 percent by weight in which a substantial portion of the barium sulfate particles have a mean diameter of at least 10 microns. This negative contrast agent provides dark imaging in a T2 weighted pulse sequence; namely a relative signal intensity (RSI) approaching zero. It also provides a relative signal intensity (RSI) of under 30 percent of that of a reference that approximates tissue in a T1 weighted pulse sequence.

What is claimed is: 
     
       1. A negative contrast agent used in magnetic resonance imaging of the gastrointestinal tract comprising: a suspension having a substantial portion of a first constituent consisting of barium sulfate particles and a substantial portion of a second constituent comprising particles selected from at least one of the group of materials consisting of pharmaceutically acceptable clays, said second constituent constituting at least two percent by weight of said suspension, a substantial portion of said barium sulfate particles having a mean diameter sufficiently large to provide a relative signal intensity substantially less than 0.5 in at least one of the MRI pulse sequence modes.   
     
     
       2. The negative contrast agent of claim 1 wherein said mean diameter of said portion of said barium sulfate particles is at least ten microns. 
     
     
       3. The negative contrast agent of claim 1 wherein said second constituent is a smectite clay. 
     
     
       4. The negative contrast agent of claim 2 wherein said second constituent is a smectite clay. 
     
     
       5. The negative contrast agent of claim 1 wherein said second constituent constitutes at least two percent by weight of said suspension. 
     
     
       6. The negative contrast agent of claim 2 wherein said second constituent constitutes at least two percent by weight of said suspension. 
     
     
       7. The negative contrast agent of claim 1 wherein at least ten percent by weight of said suspension is constituted by barium sulfate particles having a mean diameter of at least ten microns. 
     
     
       8. The negative contrast agent of claim 2 wherein at least fifteen percent by weight of said suspension is constituted by barium sulfate particles having a mean diameter of at least ten microns. 
     
     
       9. The negative contrast agent of claim 1 wherein at least twenty-five percent by weight of said suspension is constituted by barium sulfate particles having a mean diameter of at least ten microns. 
     
     
       10. The negative contrast agent of claim 7 wherein said second constituent constitutes at least two percent by weight of said suspension. 
     
     
       11. The negative contrast agent of claim 8 wherein said second constituent constitutes at least two percent by weight of said suspension. 
     
     
       12. The negative contrast agent of claim 9 wherein said second constituent constitutes at least two percent by weight of said suspension.